This invention relates generally to the field of oil well, gas well, water well and subterranean pollution remediation well equipment and, more particularly, to a device which facilitates installation of a filtering medium filtering sand and undesirable solids from fluids, gases, and toxic extraction from subterranean well bores.
Many types of screens and filtering devices are known in the art that are designed to exclude sand and other solids from fluids and gases produced from oil gas, water and pollution remediation wells without undue restriction of the production rate of fluids or gases. These devices are often used with filter aids, such as gravel and/or sand, which are either incorporated within the device or separately placed surrounding the device.
Wire wrapped screens and prepacked screens are examples of devices used inside a drilled hole. The drilled hole may be left open or may have a casing or liner cemented and perforated prior to positioning such a device. Openings in such screens may be designed to stop, or bridge undesirable solids contained in fluids or gases.
Screens and well liners are often surrounded by filter aids. The filter aids consist commonly of gravel. When used with filter aids or gravel, the openings in the screen and liners are designed to stop, or bridge, the filter aid and the filter aid is designed to stop or bridge the undesirable solids contained in the produced fluids or gases.
Prepacked screens, porous material filter devices and such are examples of devices that incorporate a filter medial in the screen body. These devices are used for the same purpose and these filter aids commonly consist of gravel.
Multiple wrapped screens provide two or more concentric wire wrappings which act as multiple filters in one device to prevent invention of undesirable solids and are often used with filter aids, such as gravel, in the well bore.
One problem that all of these prior art devices have in common is that they have no practical means for packing gravel in voids or unpacked areas of outside gravel which s produced in the screen/wellbore annulus. Such voids or unpacked areas constitute a path for undesirable sand or solids entering from the unsolidified layer to the wellbore which results in corrosion of the screen, closure of the screen opening and/or filling the inside of the wellbore with undesirable sand or solids.
Such voids or unpacked areas are produced by flowing into the inside of the screen of conveying fluid which conveys gravel through the screen/wellbore annulus when the gravel is pumped through these voids.
This causes the velocity of the conveying fluid in the space and thereby causes concentration of gravel which is generally called gravel slurry dehydration and this prevents distribution of gravel over the entire length of the screen.
This problem is particularly serious in a high angle wellbore which is inclined by 45 degrees to 90 degrees from normal, as gravity forces the gravel in the low side of the wellbore to form dunes and these dunes prevent subsequent movement of the gravel in the screen/wellbore annulus. As the gravel is heaped up, the conveying fluid flows into the screen mainly from the high side of the screen which reduces the velocity the conveying fluid and thereby reduces the capacity of the fluid to push the gravel to the bottom or lower end of the screen.
In a very long (100-2,000 feet or over) and high angle degrees to 90 degrees), the gravel is heaped up on the low side of the wellbore when the gravel is pumped and, when feeding of the gravel is completed, the upper side of the screen is left uncovered by the gravel, so that it is particularly difficult to pack gravel in such a long wellbore. Subsequently, the portion of the screen which is not covered by the gravel is exposed to corrosion by solids contained in the produced fluid or gas and the opening of the screen is easily blocked by undesirable solids.
Dehydration of gravel slurry must be controlled so that sufficient dehydration will be achieved to prevent excessive loss of the fluid in the ground or screen and pack the gravel to the degree that each grain of the gravel is in contact with another.
U.S. Pat. No. 4,945,991, Jones, L. G., "Methods for Gravel Packing Wells" discloses a screen with substantially rectangular perforated shunt tubes attached to the outside of a screen longitudinally over the entire length of the screen, and connected between all sectional lengths of screens attached together to provide flow paths for the gravel laden fluid to flow into and pack voids or unpacked areas of the screen/wellbore annulus. This device allows the gravel/fluid slurry to enter-and flow through multiple flow paths near or above the screen and to thereafter flow both down the screen/wellbore annulus or down one or more of the appendaged perforated shunt tubes. Dehydration of the slurry in the perforated shunt tubes is inhibited by combination of limited area of perforations in the tubes and by the flow of gravel slurry down the screen/wellbore annulus, thus gravel slurry in the perforated shunt tubes is much less likely to be dehydrated and is most likely to flow continuously through the shunt tubes until it reaches the vicinity of a portion of the screen/wellbore annulus that is void of gravel or is not fully packed with gravel, then the gravel slurry in the perforated shunt tubes will flow into the inadequately gravel packed annulus.
Problems with the device of U.S. Pat. No. 4,945,991 are that it is troublesome to hang down the device into wellbore, that this device prevents a desirable flow of gravel slurry in the screen/wellbore annulus and that it is difficult to lift up this device from the wellbore when the device stuck to the wellbore and/or it becomes necessary to lift the device. Besides, it is extremely difficult to connect respective shunt tubes attached to the outside of the screen to shunt tubes attached to the outside of a following screen in the course of assembling the screen and lowering it into the wellbore.
It is therefore, a first object of the invention to provide an improved well screen having a plurality of gravel slurry flow paths which is easy to assemble at a well site, is easy to hang down or up through a wellbore and does not prevent gravel slurry flow in a screen/wellbore annulus.
It is a second object of the invention to provide a well screen facilitating connection of shunt tubes of one screen with shunt tubes of an adjacent screen while the screen is assembled and lowered in a well bore.